Unitary plastic boat lift buoyancy tank

ABSTRACT

A plastic rotationally molded polyethylene buoyancy tank for boat lifts allows connection of steel to lengthwise grooves molded into each side of the buoyancy tank. Preferably, a plastic bulkhead is formed within the tank during its molding process. A segment of framing steel is bracketed between a pair of inwardly tapered compressible opposed grips. The compressible grips each have outwardly tapered slots with mating tapered rigid inserts. With the inserts partially seated on the grips, the grips are slipped lengthwise or pressed laterally into their respective grooves. Bolts extending through the grips into threaded holes in the inserts are tightened to pull the grips over their tapered inserts. This spreads and compresses the grips in their respective grooves, locking the brackets and connecting steel in place on top of the tanks.

BACKGROUND OF THE INVENTION

This invention relates generally to lifts for watercraft and moreparticularly concerns buoyancy tanks for boat lifts and the like.

Corrosion is a major concern in the manufacture and maintenance of boatlifts. Typically, boat lift buoyancy tanks are encompassed by steelwhich secures the tanks and permits connection of other components tothe lift. In use, at least parts of the steel are always submerged andconstantly exposed to a corrosive environment which leads to shortenedlift life. One method used by the industry to deal with this problem isthe use of steel inserts, such as specially threaded nuts, which aremolded into plastic parts. Since the steel must be fixed to the lift inthe specific locations and orientations dictated by the inserts, designflexibility is limited. Furthermore, these inserts are normallylongitudinally spaced on the buoyancy tanks and molded in placeperpendicular to the shrinkage plane. In the cooling phase of themolding process, as the plastic shrinks over the length of the tank, theinserts can't move with the shrinkage. This results in tank deformationand other problems.

Bulkheads are another factor impacting the manufacture and quality ofboat lift buoyancy tanks. Bulkheads are currently used in some existingbuoyancy tanks as a divider or baffle to control air and water. Becausebuoyancy tanks are made by rotational molding, the molded tank is afinished product. Access to the inside of the tank to install a bulkheadis impossible without violating the integrity of the tank. As a result,in known manufacturing processes, bulkhead installation is a timeconsuming and tedious process.

It is, therefore, an object of this invention to provide a boat liftbuoyancy tank which supports all non-plastic connections above the waterline when the lift is raised. Another object of this invention is toprovide a boat lift buoyancy tank which permits universal selection ofconnection points for the lift components along the length of the tank.A further object of this invention is to provide a boat lift buoyancytank which eliminates the need for multiple single position inserts toaccommodate connection of the lift components. Yet another object ofthis invention is to provide a boat lift buoyancy tank which hascontours adapted for connection of lift components which will not deformas a result of shrinkage during the molding process. It is also anobject of this invention to provide a boat lift buoyancy tank which hasan integral internal bulkhead formed during the tank molding process.Still another object of this invention is to provide a boat liftbuoyancy tank which eliminates the need for installing bulkheads afterthe tank is molded.

SUMMARY OF THE INVENTION

In accordance with the invention, a plastic rotationally moldedpolyethylene buoyancy tank for boat lifts allows connection of steel tolengthwise grooves molded into each side of the buoyancy tank. Thegrooves are located proximate the top of the buoyancy tank so that thesteel anchored to the grooves is fully above the water line when thelift is in its raised position. Therefore, the steel is not constantlyexposed to the corrosive environment of the water. The lengthwisegrooves allow the steel to be attached anywhere along the length of thetank, affording a high degree of flexibility in the design of the boatlift structure.

A segment of framing steel is bracketed between a pair of inwardlytapered compressible opposed grips. The compressible grips each haveoutwardly tapered slots with mating tapered rigid inserts. With theinserts partially seated on the grips, the grips are slipped lengthwiseor pressed laterally into their respective grooves. Bolts extendingthrough the grips into threaded holes in the inserts are tightened topull the grips over their tapered inserts. This spreads and compressesthe grips in their respective grooves, locking the brackets andconnecting steel in place on top of the tanks.

Preferably, a plastic bulkhead is formed within the tank during itsmolding process. The bulkhead is made from a plastic that has a slightlyhigher melting point than the tank's plastic. The plastic bulkhead isheld in place in the mold during the tank molding process. Thetemperature in the process melts the powdered plastic for the tank andalmost melts the plastic bulkhead. The two plastics fuse together aroundthe perimeter of the inner mold surface, resulting in a molded-in-placebulkhead.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is a perspective view of a preferred embodiment of the moldedplastic buoyancy tank with a plastic bulkhead molded in place;

FIG. 2 is a top plan view of the buoyancy tank of FIG. 1;

FIG. 3 is a side elevation view of the buoyancy tank of FIG. 1;

FIG. 4 is an end elevation view of the buoyancy tank of FIG. 1;

FIG. 5 is a perspective view of a preferred embodiment of the grips usedto secure float framing components to the buoyancy tank;

FIG. 6 is a perspective view of a preferred embodiment of the insertsused with the grips of FIG. 5;

FIG. 7 is an end elevation assembly view of the grips and inserts ofFIGS. 5 and 6;

FIG. 8 is a perspective view of a preferred embodiment of a bracketassembly for use with the grips and inserts of FIGS. 5 and 6;

FIG. 9 is a cross-sectional view taken in a plane transverse to thelength of the tank at one stage of float assembly;

FIG. 10 is a cross-sectional view in a plane transverse to the length ofthe tank at a subsequent stage of float assembly;

FIG. 11 is a perspective view of a float using the tanks, grips andinserts of the present invention; and

FIG. 12 is an exploded sectional view illustrating the bracket assemblyof FIG. 8 mounted on the buoyancy tank.

While the invention will be described in connection with a preferredembodiment and method, it will be understood that it is not intended tolimit the invention to that embodiment or method. On the contrary, it isintended to cover all alternatives, modifications and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims.

DETAILED DESCRIPTION

Turning first to FIGS. 1-4, a preferred embodiment of the rotationallymolded polyethylene buoyancy tank is illustrated. The tank 10 is anelongated shell having a substantially flat top wall 11 with a raisedportion 12. The flat outer portions of the top wall 11 are desirable forabutment with brackets as will be hereinafter explained. The raisedportion 12 of the tank 10 affords an irregular cross-section for the topwall 11, thus affording additional strength to the tank 10. The tank 10also has side walls 13 and 14 and an arcuate bottom wall 15. The shellis completed by end walls 16 and 17. Each side wall 13 and 14 isprovided with a lengthwise groove 18 and 19, respectively, extendingsubstantially for the entire length of the sidewalls 13 and 14 andproximate the top wall 11. The tank 10 is also provided with one or moreair inlet/outlet passages 21 and water inlet/outlet passages (notshown). As shown in FIG. 1, one or more bulkheads 22 may be providedwithin the tank 10 for the purpose of controlling the flow of air andwater in the tank 10.

Preferably, the tank is molded of polyethylene or other suitable plasticby a rotational molding process. In the molding process, the bulkhead 22is secured in the tank mold at the beginning of the process. The plasticpowder for the tank 10 has a melting temperature which is lower than theprocess temperature at which the tank 10 is molded. The bulkhead 22, onthe other hand, is preformed from plastic having a melting temperatureslightly higher than the process temperature. Therefore, as the tank 10is molded at the process temperature, the tank 10 and the bulkhead 22are fused together along the perimeter 23 of the bulkhead 22. As shown,the bulkhead 22 is transverse to the length of the tank 10 and disposedapproximately at its midpoint. However one or more bulkheads can be usedin any position or orientation.

Looking at FIGS. 1, 4 and 12, the configuration of the grooves 18 and 19is best seen. The grooves 18 and 19 have top 24 and 25 and bottom 26 and27 walls, respectively. The grooves 18 and 19 are opposed to each otherso that the top 24 and 25 and bottom 26 and 27 walls extend inwardlyinto the tank 10 to side walls 28 and 29, respectively. Preferably, asshown, the groove top 24 and 25 and bottom 26 and 27 walls arenarrowingly tapered or converging toward the groove side walls 28 and29, respectively. A taper angle of approximately two degrees relative tohorizontal is suitable.

Looking now at FIGS. 5, 7, 8 and 12, a grip 30 for use with the grooves18 and 19 is illustrated. The grip 30 is a resiliently compressiblemember having a back wall 31 with a rigid plate 32 inset in the backwall 31 along the length of the grip 30. The side walls 33 and 34 of thegrip 30 are inwardly narrowingly tapered from the back wall 31 to thefront wall 35 so that, in exterior cross section, the grip 30 issubstantially trapezoidal. A recess 36 is provided in the grip 30through the front wall 35. The recess 36 is wideningly or outwardlytapered toward the back wall 31. The recess taper angle of two to threedegrees relative to horizontal is suitable. The end walls 37 and 38 haveslots 39 and 41 extending from the front wall 35 toward the back wall 31to permit the front wall 35 and back wall 31 to be more manipulablerelative to each other. One or more smooth holes 42 and 43 extendthrough the plate 32 and the back wall 31 into the recess 36.

Looking at FIGS. 6, 7, 8 and 12, a rigid insert 44 having a trapezoidalcross-section is tapered for insertion into the recess 36 in the grip30. Preferably, the taper of the cross-section of the insert 44 is at asteeper angle than the taper of the recess 36. This can best be seen inFIG. 7. The insert 44 is provided with one or more threaded holes 45 and46 which align with the smooth holes 42 and 43 in the grip 30 when theinsert 44 is inserted into the recess 36 in the grip 30. Bolts 47 and 48extending through the holes 42 and 43 in the grip 30 and threadedlyengaged in the holes 45 and 46 in the insert pull the rigid insert 44into the recess 36 as they are rotated. Preferably, the plate 32 and theinsert 44 are made of aluminum and the grip 30 is made of moldedpolyurethane.

Looking now at FIG. 8, the use of the grips 30 to secure a segment ofthe framing steel 51 of the boat lift to the tank 10 is illustrated. Asshown, a section of framing steel 51 such as an angle iron issufficiently long to extend substantially across the top wall 11 of thetank 10. A 3″×2″×{fraction (3/16)}″ steel angle iron is suitable. Theends of the framing steel 51 are connected to brackets 52 and 53,possibly formed from ¼″ steel. As shown, spacers 54 and 55 are weldedbetween the brackets 52 and 53 and the framing steel 51 if necessary topermit the framing steel 51 to ride over the raised portion 12 of thetank 10 when the horizontal portions 56 and 57 of the brackets 52 and 53are seated on the flat top wall 11 of the tank 10. The brackets 52 and53 extend downwardly to grip mounting portions 58 and 59. The gripmounting portions 58 and 59 have holes (not shown) for the bolts 47 and48 to extend through the brackets 52 and 53 into the rigid plates 32 inthe grip 30.

Looking now at FIGS. 9, 10 and 12, the manner of mounting the segment offraming steel 51 to the tank 10 will be explained. Inserts 44 areinserted into the recesses 36 in grips 30 so as to hold these componentstogether without significantly deforming the grips 30. One grip 30 withits insert 44 is then inserted into each groove 18 and 19 in the tank 10with the inserts 44 against the side walls 28 and 29 of the grooves 18and 19. The grips 30 are aligned lengthwise in the grooves 18 and 19 atthe position at which it is desired to secure the segment of framingsteel 51 to the tank 10. The brackets 52 and 53 welded to the framingsteel 51 are aligned with the grips 30 seated in the grooves 18 and 19.As shown in FIG. 9, the holes in one of the brackets 53 are aligned withthe holes 42 and 43 in its grip 30. The bolts 47 and 48 are insertedthrough the bracket 53, the rigid plate 32 and the back wall 31 of thegrip 30 into the threaded holes 45 and 46 in the insert 44. The boltsare then tightened to pull the insert 44 deeper into the recess 36 untilthe front wall 35 of the grip 30 is brought into contact with the sidewall 29 of the groove 19. The insert 44 compresses the side walls 33 and34 of the grip 30 against the top and bottom walls 25 and 27 of thegroove 19 to lock the grip 30 in the groove 19. As seen in FIG. 10, theholes in the other bracket 52 are then aligned with the holes 42 and 43in the other grip 30 and the process repeated to secure the other grip30 in place in its groove 18. With the grips 30 so secured, the segmentof framing steel 51 is secured in position atop the top wall 11 of thetank 10. As shown, the segment of framing steel 51 is provided with aplurality of holes 61 to facilitate connection of additional framingsteel to the tank 10.

Turning to FIG. 11, a boat lift is illustrated in which two tanks 10 inparallel alignment have framing steel secured thereto by use of theparallel grooves 18 and 19 in the upper side walls 13 and 14 of thetanks 10. All of the steel is fixed at or above the level of the grips30 so that all of the steel will be above the water line when the boatlift is in a raised condition. Since the grooves 18 and 19 extend forsubstantially the entire length of the tanks 10, the grips 30 andtherefore the framing steel 51 can be positioned at any desirablelocation along the length of the tanks 10. This affords a great deal offlexibility in the design of the lift so that the lift structure can beeasily contoured to suit any configuration of water vehicle using thesame tanks 10.

Thus, it is apparent that there has been provided, in accordance withthe invention, a boat lift buoyancy tank and a method for making thetank that fully satisfy the objects, aims and advantages set forthabove. While the invention has been described in conjunction with aspecific embodiment and method, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart and in light of the foregoing description. Accordingly, it isintended to embrace all such alternatives, modifications and variationsas fall within the spirit of the appended claims.

What is claimed is:
 1. A buoyancy tank for a boat lift comprising anelongated plastic shell having a pair of opposed lengthwise grooves inupper portions of sidewalls of said tank, each of said grooves havingtop and bottom walls extending inwardly to a side wall thereof, saidgroove top and bottom walls being narrowingly tapered toward said grooveside wall.
 2. A buoyancy tank for a boat lift comprising an elongatedplastic shell having a transverse bulkhead therein formed by moldingsaid tank with said bulkhead secured therein at a process temperature,said tank being molded from plastic having a melting temperature lowerthan said process temperature and said bulkhead being formed fromplastic having a melting temperature slightly higher than said processtemperature whereby said tank and said bulkhead are fused together alonga perimeter of said bulkhead, said shell having a pair of opposedlengthwise grooves in upper portions of sidewalls of said tank, each ofsaid grooves having top and bottom walls extending inwardly to a sidewall thereof, said groove top and bottom walls being narrowingly taperedtoward said groove side wall.